Contribution of magnetotail reconnection to the cross-polar cap electric potential drop

Loading...
Thumbnail Image
Journal Title
Journal ISSN
Volume Title
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2011
Department
Major/Subject
Mcode
Degree programme
Language
en
Pages
10
Series
Journal of Geophysical Research: Space physics, Vol. 116, nro A08219
Abstract
Since the work of Dungey (1961), the global circulation pattern with two (dayside and nightside) reconnection regions has become a classic concept. However, the contributions of dayside and nightside sources to the cross-polar cap potential (PCP) are not fully understood, particularly, the relative role and specifics of the nightside source are poorly investigated both in quantitative and qualitative terms. To fill this gap, we address the contributions of dayside and nightside sources to the PCP by conducting global MHD simulations with both idealized solar wind input and an observed event input. The dayside source was parameterized by solar wind–based “dayside merging potential” Φd = LeffVBt sin4(θ/2), whereas to characterize the nightside source we integrated across the tail the dawn-dusk electric field in the plasma sheet (to obtain the “cross-tail potential” Φn). For the idealized run we performed simulations using four MHD codes available at the Community Coordinated Modeling Center to show that contribution of the nightside source is a code-independent feature (although there are many differences in the outputs provided by different codes). Particularly, we show that adding a nightside source to the linear fit function for the ionospheric potential (i.e., using the fit function Φfit = KdΦd + KnΦn + Φ0) considerably improves the fitting results both in the idealized events as well as in the simulation of an observed event. According to these simulations the nightside source contribution to the PCP has a fast response time (<5 min) and a modest efficiency (potential transmission factor from tail to the ionosphere is small, Kn < 0.2), which is closely linked to the primarily inductive character of strong electric field generated in the plasma sheet. The latter time intervals are marked by strongly enhanced nightside (lobe) reconnection and can be associated with substorm expansion phases. This association is further strengthened by the simulated patterns of precipitation, the R1-type field-aligned substorm current wedge currents and Hall electrojet currents, which are consistent with the known substorm signatures.
Description
Keywords
magnetosphere-ionosphere coupling, magnetospheric convection, polar cap potential, substorm
Other note
Citation
Gordeev, E. I. & Sergeev, V. A. & Pulkkinen, Tuija I. & Palmroth, M. 2011. Contribution of magnetotail reconnection to the cross-polar cap electric potential drop. Journal of Geophysical Research: Space physics, Vol. 116, nro A08219. P. 10. 2156-2202 (electronic). DOI: 10.1029/2011JA016609.